WSP08775

• File Number: 8056
• Description: Drought Preparedness
• State: CO
• Basin: Statewide
• Date: 1/1/1979
• Author: USGS
• Title: Hydrologic and Human aspects of the 1976-77 Drought
• Water Supply Pro - Doc Type: Report/Study

n ." "f'f"'S'
'J .) ;,/ ,.J ,J

25

90"

85"

CHRONOLOGY OF THE 1976-77 DROUGHT

75'

48'

t

WISCONSIN

44'

o
I
o

80.

EXPLANATION

- Region boundary

44.

PENNSYLVANIA

40'

'"0
I

200 KI LOMETERS
I
I
100 MILES

Figure 9. Great Lakes-WRC Region 04.

but rainfall for June through October 1977
ranged from 75 to 150 percent of normal.
The Palmer index (see figs. 6 and 7) re-
flects the precipitation distribution in time
and space mentioned above and the fact that
above normal precipitation did not always end
drought conditions because agriculture is de-
pendent upon rain at roughly weekly intervals
as well as an adequate amount of rain. No
significant rain fell in Wisconsin between
Apri115 and May 11, 1977. The Palmer index
for the Upper Peninsula of Michigan dropped
to -4 or lower in August 1976 and stayed near
that for more than a year. Values this low
indicate extreme drought conditions. Northern
Wisconsin and northeastern Minnesota had Pal-
mer indexes ranging from -4 to -9 at one time
or another between August 1976 and August
1977.
Above normal temperatures during the
summer of 1976 intensified the drought con-
ditions primarily by reducing the soil moisture.
Then the very low temperatures during the
severe winter of 1976-77 made it necessary to

run water through pipes to keep them from
freezing and further taxed the dwindling water
supply and the pumping capacity of a few
cities. Unseasonably high temperatures and
strong winds the latter part of April 1977 in
Wisconsin reduced the soil moisture to 25 per-
cent of normal.
The low precipitation in 1976, the very cold
winter of 1976-77, and the continuation of
below normal precipitation in 1977 were a
series of events in which each succeeding
event compounded the effects of the earlier
events. Together they made the drought the
most serious one in at least 50 years in Michi-
gan, Minnesota, and Wisconsin.
The runoff pattern in Wisconsin reflected
the precipitation pattern very closely. By
early August 1976, the flows in the northwest
basins had dropped to amounts that past
records show have been exceeded 92 percent
of the time. Flows in the Fox-Wolf River
basin south and west of Green Bay were
approaching the 10-yr low flow by late August
1976.